In only one of the 27 cases reviewed by the Union-Tribune did county officials acknowledge that mistakes were made. That was in the death of Mariah Leon.

In March 2000, the first month of her life, Mariah was taken to the hospital twice. At first doctors could not say for sure if she had been abused, but on the second visit – when they found a head injury and broken bones in her leg – they were certain.

Mariah was removed from her home and placed in foster care, where she healed and thrived.

Child welfare officials were unable to determine who was responsible for the injuries. Mariah lived with numerous adults, and both parents passed lie-detector tests denying the abuse.

So, child welfare officials headed down a different track, offering the parents lots of services and training classes. The goal of the dependency system is to try to reunite families whenever possible.

Things seemed to go well. Gradually, the parents were given supervised visits with Mariah.

Those went well, too, and by October 2000 the parents were allowed unsupervised visits with the baby. That same month, a social worker noticed a red mark on Mariah's ear and a scratch on her finger, but took no action.

In January 2001, the social worker noticed “a little bruise on the forehead.” The baby's father, Daniel Leon, said it happened when he took the child out of the car.

A Jan. 12 court report was hopeful. “There is a substantial probability that Mariah will be returned by July 18, 2001,” the social worker wrote.

Two days later, Mariah was at Children's Hospital in an irreversible coma, which doctors concluded was a result of being violently shaken. After four months on life support, she died.

While prosecutors pursued their case against Daniel Leon, social workers conducted their own private review. It concluded that the system moved too quickly to reunite the family. One “key staff person” retired after the review.

“I think overall there was an acknowledgment that more safeguards were needed in making a decision like this,” said Mary Harris, the head of Child Welfare Services for the county.

Now, the agency has a special process for cases identified as high-risk, and major decisions – such as allowing unsupervised, overnight visits – have to be approved by upper-level managers.

Daniel Leon was convicted in May 2002 of assault causing the death of a child under 8 years old and is serving a 42-year prison sentence.